The present invention relates generally to a joint forming apparatus and specifically to a die and punch for forming a joint between sheets of material.
It is common within the metal forming industry to join pieces of sheet metal by punching or otherwise deforming them to cause an interlocking relationship in a localized area. However, these traditional joints have typically required shearing of the sheet material. Thus, these joints tend to leak and also have their corrosion resistant coatings destroyed.
More recently, an apparatus has been used for joining two or more sheets of material together by creating a leakproof and secure joint. These improved conventional joints are created by use of a punch acting against an anvil to produce what is known as a TOG-L-LOC® joint therebetween. Such a leak proof joint and tooling are disclosed in U.S. Pat. Nos. 5,267,383 and 5,177,861, both of which are entitled “Apparatus for Joining Sheet Material” and issued to Sawdon. The disclosures of these patents are incorporated by reference herewithin.
The conventional TOG-L-LOC® leak proof joints consist of two or more sheets of material having a button or joint formed therebetween by a uniformly cylindrical punch forcibly pushing a punch side sheet of material into interlocking engagement with a die side sheet of material. These conventional leakproof joints have seen tremendous commercial success for use in varied applications such as steel microwave ovens and aluminum automotive bodies.
The apparatus includes a punch assembly and a die assembly which are arranged on opposite sides of the sheet material to be joined. The die assembly includes an anvil that is surrounded by one or more radially moveable die blades. The die assembly may also include a rigid shield that coaxially and radially surrounds the anvil and the one or more die blades. The conventional die assembly also includes a coiled or bias spring to radially inwardly retain the one or more moveable die blades against the anvil while allowing movement radially outward during joint formation. Such a die assembly and apparatus are disclosed in U.S. Pat. No. 5,727,302, entitled “Die and Punch For Forming A Joint and Method of Making The Die,” issued to Sawdon, and incorporated by reference herein. However, the use of the bias spring is not without drawbacks. For example, the bias spring is susceptible to trapping factory dirt and debris. The bias spring also requires the step of welding which increases production time and costs. Additionally, the bias spring may break where the wire is joined by welding. If this breakage occurs, the one or more die blades that were held against the anvil can become loose and fall out of the die assembly. Therefore, it is desirable to provide a retaining means that does not need to be concerned with weld durability and is less susceptible to trapping factory dirt and debris.
In accordance with the present invention, a flexible retainer for retaining die blades in a tool assembly is disclosed. The retainer comprises axially opposite top and bottom surfaces with an outer wall extending axially therebetween and having an outer axial length. The retainer has an inner wall that is generally concentric with and radially spaced inward from the outer wall. In another aspect of the present invention, a central opening in the retainer is configured and adapted to extend radially around the die blades so that the retainer retains the die blades in the die assembly while allowing radial movement of the die blades. A further aspect of the present invention provides a retainer with at least one channel that extends axially between the inner and outer walls.
In yet another aspect of the present invention, a die assembly for forming a joint between sheets of material is disclosed. The die assembly comprises an anvil, at least one die blade disposed adjacent the anvil, a flexible retainer, and a shield that coaxially and radially surrounds the anvil.
In yet another aspect of the present invention, a die retainer is colored or otherwise identified to correspond to a size of the die blade(s) so that the size of the die blade can be visually ascertained.
A method of making a die assembly that is used for forming a joint between at least two sheets of material is also provided.
The present invention is advantageous over prior constructions since the present invention is self cleaning of debris during operation. The present invention is further advantageous since the retainer is less expensive to manufacture and simple to assemble. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.